[Wikipedia] Japan & Russian native, Description: Reynoutria sachalinensis (giant knotweed or Sakhalin knotweed syns. Polygonum sachalinense, Fallopia sachalinensis) is a species of Fallopia native to northeastern Asia in northern Japan (Hokkaido, Honshu) and the far east of Russia (Sakhalin and the southern Kurile Islands).[2] Stem and inflorescence The leaves are some of the largest in the family, up to 15 to 40 cm (6 to 15.5 in) long and 10 to 28 cm (4 to 11 in) broad, nearly heart-shaped, with a somewhat wavy, crenate margin. The flowers are small, produced on short, dense panicles up to 10 cm (4 in) long in late summer or early autumn; it is gynodioecious, with male and female (male sterile) flowers on separate plants. (link added by Mary Ann Machi)